TWI811264B - Printed circuit board for a radar level measurement device with waveguide coupling - Google Patents

Abstract

The invention relates to a circuit board (10) with a circuit board substrate (12) for a radar level measurement device, wherein a microwave signal is coupled into a waveguide (14) via a microwave conductor (16). A connection area (22) on the front side (18) of the circuit board substrate (12) is used to accommodate the waveguide (14). The shape of the resonant basin is produced inversely by making an annular circumferential groove (30) at the rear side (28) of the circuit board substrate (12), wherein the walls of the groove (30) have an electromagnetic reflective coating (32) . The groove (30) together with the region (34) at the rear side (28) surrounded by the groove form a resonator for the coupled microwave signals.

Description

Circuit board for radar level measurement device with waveguide coupling device

The invention relates to the measurement of a level in a container, for example. In particular, the invention relates to a circuit board for a microwave-based or radar-based level measurement device having a microwave coupling device in a waveguide.

Known material level measuring devices increasingly use the principle of determining material level by utilizing the propagation of electromagnetic waves or the reflection characteristics and propagation time characteristics of such waves. Here, high-frequency electromagnetic waves (for example, microwave pulses) are transmitted from the level measuring device in the direction toward the surface of the filler in the container. The high-frequency electromagnetic waves are reflected by the surface, and based on the propagation time of the reflected microwave signal, Calculate level. With the further development of technology, especially with the development of electronics and semiconductor technology, higher frequencies in the range of fifty to one hundred megahertz (oberen zweistelligen Gigahertzbereich) are increasingly used for level measurement. In particular, the high frequencies and the resulting physics of wave propagation increase the demands placed on the high-frequency components of such level measuring devices. In such cases, high-frequency components are often formed on circuit boards containing electronics and antenna devices for generating microwave pulses.

For example, one way of transmitting the generated high-frequency waves to an external antenna is the connection of a waveguide. Advantageously, such waveguides can be used to convey microwave signals in the frequency range of use. A particular challenge lies in waveguide transitions, that is, the transmission of electromagnetic waves from a conductor (for example, on a circuit board) to the inside of a waveguide and vice versa. For example, the conductor can be designed as a microstrip, the ends of which are inserted into the waveguide. For example, the waveguide can be designed as an air waveguide.

In order to achieve electrical losses and good adaptability, technical precautions may be particularly necessary in such cases. So, for example, a waveguide must have resonators at its ends to couple signals with low or no loss, the size, diameter and geometry of the resonators being designed to minimize losses over the frequency range of use. At the same time, it is desirable to reduce component size and simplify construction while maintaining high quality. The technical solution to the problem consists in integrating as many functions as possible and thereby obtaining simple and cheap components. For example, EP1949491B1 discloses a waveguide transition piece in which the resonator of the waveguide is integrated into the circuit board.

The following embodiments can improve the mechanical stability, electromagnetic reliability and accuracy of radar-based or microwave-based level measurement devices. At least some of the embodiments described below are based on the idea that in today's known solutions a resonator is required which is usually designed as a basin. At the same time, such resonators need to be spatially configured directly at the end of the waveguide to achieve lossless or low-loss waveguide termination. At this time, if the waveguide is conventionally introduced to the circuit board at an angle of 90°, the circuit board needs to be inserted in the direction toward the substrate of the circuit board. For example, in the prior art, this could be achieved by cutting or milling in a layer of the circuit board substrate located in the extension of the waveguide. However, usually, the layer of the circuit board substrate had to be made of a high frequency substrate or plastic. The cover consists of a cover to seal to avoid contamination. This may have disadvantages in terms of the electrical, electromagnetic and mechanical properties of the circuit board.

To this end, as a solution, a circuit board for a radar level measurement device is proposed, which circuit board has a non-conductive planar circuit board substrate as a supporting material. In addition to its mechanical stabilization and support functions, the circuit board substrate is designed to be insulated for the electromagnetic wave frequency range used. For example, the circuit board substrate may be a so-called high-frequency substrate. A microwave conductor for coupling microwave signals into the waveguide is disposed on the circuit board substrate. For example, the microwave conductor can be designed as a microstrip conductor. In one example, the microwave conductor is disposed on a surface of a circuit board substrate. In another example, the microwave conductors extend at least partially within the circuit board substrate.

A circumferential, ie annular (eg circular or square) connection area is arranged on the front side of the circuit board substrate for accommodating the front end of the waveguide. For example, under normal circumstances, the circuit board substrate is designed as a support plate or base plate, which is usually a composite piece made of a high-frequency substrate and a basic support body (eg, FR4). For example, the front side can be defined to have components by the design of such planes. Accordingly, the rear or lower side is usually provided with contact portions and connecting portions.

In other words, an annular connection area is an area on the front side of the circuit board substrate which, for example, is in direct contact with the waveguide or a wall of the waveguide or allows a separate mechanical accommodation. An annular shape here is to be understood as meaning that this region is adapted at least partially to the cross-sectional shape of the waveguide with respect to its customary shape. For example, if the cross-sectional shape of the waveguide is circular, the connection area is also modeled to be approximately circular.

In one example, the connection area is designed to be rectangular in order to accommodate a waveguide with a rectangular cross-section. The waveguide can be fixed mechanically by separate mechanical mechanisms or also in combination with electrical joints. For this purpose, the waveguide can be glued, screwed or welded to the connection area, for example.

The end of the microwave conductor protrudes into the connection area so that microwave signals can be transmitted from the microwave conductor to the waveguide and vice versa. In one example, the ends of the microwave conductors are at approximately the center of the waveguide cross-section. In other words, the end of the microwave conductor has a function similar to that of an antenna, which is used to transmit microwave signals into the waveguide or receive microwave signals from the waveguide. In one example, the microwave conductors are disposed within the circuit board substrate, thereby eliminating the need to form separate gaps at the ends of the waveguides for insulating the microwave conductors.

For example, on the rear side of the circuit board substrate, a circumferential groove corresponding to the cross-section of the waveguide and having an annular shape is arranged in a direction toward the waveguide with respect to the annular connection area. In principle, the cross-section of the connection region can be stepped relative to the cross-section of the waveguide, since the latter cross-section is filled with dielectric and can therefore be made smaller.

In other words, the groove extends on the rear side of the circuit board substrate and is opposite the area where the waveguide wall abuts the front side of the circuit board substrate. The purpose here is to reduce the distance between the rear surface of the circuit board substrate and the waveguide. The grooves should be provided over the largest possible area of the waveguide wall, ideally over its entire area. The resulting structure takes on an approximately basin-like shape, which ultimately forms the shape of a resonator or resonator basin. In other words, here, contrary to known solutions, a resonator geometry is produced in a negative form, or inversely (ie on the rear side of the circuit board substrate).

Where necessary, the grooves do not have to have a closed shape, but various shapes such as grooves, notches, slits and their equivalents are also conceivable. It is also not necessary to implement a closed annular shape absolutely, but rather, according to one example, the groove can be composed of segments, partial arcs or a combination of different shapes. In one example, the groove is designed as an open arc or as an open rectangular shape.

The walls of the groove and the area on the rear side of the circuit board substrate surrounded by the groove have a microwave reflective coating so that together they form a resonator for the coupled microwave signals. In other words, a substantially basin-like shape is formed by the groove and the area surrounded by the groove, a so-called resonant basin serving as the electromagnetic termination of the waveguide. Resonance occurs in the relevant frequency range due to the geometry and size and due to the reflective coating. In one example, the coating in the grooves and the coating in the area surrounded by the grooves are connected to each other. In another example, the coating and the surrounding area in the groove are separated from each other.

In one embodiment, the reflective coating is designed as a metallic coating. The metal coating can be made of various materials, preferably, it is made of metal with good conductivity in order to achieve electromagnetic and reflective effects. The advantages of metal coatings can be good accessibility and durability. In a further embodiment, a through-contact is provided between the front side and the metal coating at the groove region, enabling the metal coating to be electrically connected to the waveguide. In other words, an electrical connection is formed between the resonant basin and the waveguide wall, which is designed, for example, in a metallic manner.

Electrical connection with the other side of the circuit board substrate can be achieved through the through-contact portion. In such cases, the stability of the circuit board substrate can be maintained simultaneously by means of through-contacts, for example designed as conductive metallized holes, and at the same time sufficient performance of the electrical connection can be achieved. For example, on the front side, the connection between the through-contact and the waveguide can be formed by welding or soldering.

In one embodiment, the distance between two adjacent through contacts is less than one quarter of the microwave wavelength. This can advantageously prevent microwaves from propagating from the inner area of the waveguide or from the inner area of the connection area to areas outside the waveguide. That is, in the electromagnetic field, each adjacently arranged through-contact portion functions as a continuous barrier against microwaves as a whole.

In one embodiment, the area of the rear side surrounded by the groove is recessed in the direction towards the front side. This can be achieved, for example, by mechanical abrasion of the area. The distance of such areas with microwave reflective coatings relative to the waveguide is thereby reduced. For example, the degree of depression can achieve electromagnetic tuning of the resonant basin at the frequency of use. In another embodiment, the groove and/or the area surrounded by the groove is filled with synthetic resin. This has the advantage that the original thickness of the circuit board substrate can be restored by casting and thus the mechanical stability of the entire circuit board substrate and the circuit board can be improved. The resonant pot can be mechanically maintained on the remaining circuit board layer without such filling. Its suitability depends, for example, on the dimensions of the groove.

In addition, the recessing of the area surrounded by the grooves can allow the accommodation of the synthetic resin layer in the abraded area and create additional stability due to the synthetic resin filling in the grooves. In one example a filling of synthetic resin was carried out, thereby reestablishing the original planar surface structure of the rear side of the circuit board substrate.

In one embodiment, the connection area and groove are designed to be rectangular. This has the advantage that circular or annular waveguides can also result from waveguides with a rectangular cross-section. Accordingly, in another embodiment a circular design of such connection areas and grooves is proposed. In such cases, according to another embodiment, the circuit board may have a plurality of conductive layers, for example made of copper.

According to another embodiment, the circuit board is designed as a Land Grid Array or a Ball Grid Array. This means, for example, that contact pads are provided at the rear side of the circuit board substrate for contact with other components and components. Additionally, this can advantageously enable circuit board designs to be implemented in SMD construction. According to one example, connections to the circuit board or circuit board substrate lead to the rear side of the circuit board substrate and are connected to the contact pads. This can, for example, be connected to other components by soldering connections.

According to another embodiment, the circuit board has a plurality of conductive layers.

According to another example, the circuit board substrate is surrounded by plastic. Such plastics can advantageously form the housing function and simultaneously achieve stability and small assembly dimensions. According to another embodiment, the circuit board substrate is surrounded by plastic such that the connection areas are recessed. This therefore enables the waveguide to be in electrical and mechanical contact with the through-contact or circuit board substrate despite being surrounded by plastic.

According to one embodiment, the circuit board has a further recess for receiving high-frequency chips (HF-Chips) on the front side of the circuit board substrate, wherein the microwave conductor extends between the further recess and the connection area. The semiconductor wafer is placed in another recess and is in turn closed by a so-called glob-top or cover.

This arrangement is well suited for transmitting microwave signals from the high-frequency chip into the waveguide by having the microwave conductor on or within the circuit board substrate lead into the internal region of the waveguide.

Therefore, in the case of low losses and a compact mechanical structure, another groove, for example spatially arranged directly in the vicinity of the connection area, can be advantageously used to enable the circuit board to also function as a functional unit for generating and processing high-frequency electromagnetic signals. Receive high frequency signals. This has the advantage that the technically sensitive high-frequency component is integrated compactly and hermetically into the component and is thus maximally independent of external influences. According to one example, the high-frequency chip can also be disposed on the circuit board substrate without another groove. According to one embodiment, the other groove is filled with synthetic resin. Advantageously, this can contribute to mechanical stability and protection against environmental influences.

According to another aspect, a method for fabricating a resonator for microwaves in a circuit board is provided. First, the method includes the step of providing an electrically non-conductive planar circuit board substrate. In the next step, an annular circumferential groove is produced on the rear side of the circuit board substrate. According to an example, the groove can be composed of multiple parts, however preferably the groove can be designed as a closed ring. Then, a microwave reflective coating is coated on the wall of the groove on the rear side of the circuit board substrate and the area surrounded by the groove. For example, the coating may be a metal layer, wherein various methods for coating a metal layer on the surface of a circuit board substrate have been disclosed in the prior art. In one example, only part of the surface of the wall and/or part of the area surrounded by the groove has a metallic or at least reflective coating.

In a further step, a through-contact is produced between the front side of the circuit board substrate and the reflective coating in the recess, wherein the through-contact is arranged on the front side such that the end face of the waveguide end is electrically contactable with the through-contact connection. For example, these through-contacts can be designed as tubular holes that are subsequently metallized. Additionally, in one method embodiment, the production of the grooves includes abrasion of the circuit board substrate such that the area surrounded by the grooves is recessed in a direction toward the front side. For example, the final shape and dimensions of the resonator can thereby be generated (eg during electromagnetic tuning). According to one example, this can also be achieved by adjusting the shape and size of the groove on the rear side of the circuit board substrate.

In one method embodiment, the grooves and/or the surrounded areas are produced by means of milling. In the case of small dimensions, which are advantageous here, such a method can produce the desired shape more accurately while also having advantages in terms of efficiency. According to another method embodiment, the grooves and/or the area surrounded by the grooves are filled with synthetic resin. For this purpose, for example, heated and flowing synthetic resin can be applied to the circuit board substrate by a casting method or a spraying method (eg by a hole filling method) and can thus compensate for the abraded or milled areas. The advantage here lies in improved stability since the intended breaking point can be avoided by a thinner point and, at the same time, the synthetic resin can be stably and continuously connected to the circuit board substrate.

It will be understood that, as described above and below, a method may also be characterized by a circuit board, and vice versa.

FIG. 1 shows a portion of the circuit board 10 for the coupling waveguide 14 . Microwave conductor 16 is arranged on circuit board substrate 12 . In the example shown here, the microwave conductor 16 extends over the surface of the circuit board substrate 12 , here the microwave conductor 16 extends over the front side 18 . According to one example (not shown here), the microwave conductor 16 is disposed inside the circuit board substrate 12 . This has the advantage that, contrary to what is shown in FIG. 1 , the waveguide 14 does not need to be additionally separated or shortened at this location for insulation purposes, but rather the waveguide 14 has circumferentially planar or flat end faces, which have the advantage of being simple. manufacturing (e.g., cutting).

The circuit board substrate 12 is made of a material that is insensitive to high frequencies or is insulating for the relevant high frequency range (for example, LCP or PTFE substrates from different manufacturers). A plurality of conductive layers 20 are disposed inside the circuit board substrate 12 to form respective electrical connections of the electronic circuit. The connection area 22 defines an area of the front side 18 of the circuit board substrate 12 which faces the waveguide 14 or where the waveguide 14 is connected to the circuit board substrate 12 . This connection area 22 is designed to be circular, so that this area can accommodate the front end 26 of the waveguide 14 . According to one example, the connection area 22 is designed as a rectangle. This allows, for example, a connection to a waveguide 14 that is also designed to be rectangular. Here, it should be noted that the waveguide 14 and the connection area 22 may have various cross-sectional shapes, where it is important that the walls of the waveguide 14 and the connection area 22 overlap or directly abut each other.

The end 24 of the microwave conductor protrudes into the connection area 22 so that the microwave signal can be transmitted from the microwave conductor 16 or through the end 24 of the microwave conductor to the waveguide 14 and vice versa. In other words, the end 24 of the microwave conductor 16 serves as a transmitting and receiving antenna that transmits microwave signals into the waveguide 14 and is capable of receiving microwave signals from the waveguide 14 . On the rear side 28 of the circuit board substrate 12 , a circumferential groove 30 is arranged opposite the annular connection area 22 , which circumferential groove 30 corresponds to the cross-section of the waveguide 14 . The spatial design of such grooves is shown in the following figures.

The walls of the recess 30 are coated with a metallic coating 32 , which is shown here in dashed lines. In principle, in addition to metallic coatings, other types of coatings or materials that are reflective of microwaves in the gigahertz range involved here can generally be present here. Additionally, for example, liquids or even gases having separate physical properties or components such as ions may also be included. A metallic coating 32 may be advantageous here since it can be produced more cost-effectively than known methods and exhibits good reflective effects. In an example, groove 30 has a width of approximately 1 mm and a depth and length in the range of less than 1 mm. Here, the dimensions are set based on the microwave frequency range used. According to one example, the thickness of metal coating 32 is on the order of a few microns.

The recessed region 34 is surrounded by the groove 30 and together with the groove 30 forms a resonator or resonator basin that cooperates with the waveguide 14 on its side facing the front side 18 . According to an example, the recessed area 34 may also have a metal coating 32 without being recessed. The advantage of a recess here is that the space formed can be cast with synthetic resin 36 together with the recess and thus the stability of the circuit board 10 can be increased. Other filling, stable and durable materials such as plastics, adhesives, fillers or the like can also be used instead of synthetic resin.

A through-contact 38 is provided in the circuit board substrate 12 and is configured such that it forms an electrical connection between, for example, a metal wall of the waveguide 14 and the metal coating 32 of the rear side 28 of the circuit board substrate 12 . For example, this can also be achieved in the following manner: the through contact portion is in contact with a partial area of the conductive layer 20 , and the conductive layer 20 is in electrical contact with the waveguide 14 . Here, the waveguide 14 can be fixed to the circuit board 10 or the circuit board substrate 12 through various mechanisms, such as soldering, welding or adhesive.

A cross-sectional view of a circuit board 10 with a waveguide 14 is shown in FIG. 2 . The circuit board substrate 12 has a plurality of conductive layers 20 . An annular circumferential groove 30 is formed on the rear side 28 of the circuit board substrate 12 . Here, it can clearly be seen that the groove extends on the rear side 28 of the circuit board substrate 12 towards the front end 26 of the waveguide 14 . Here, the diameter of the recessed area 34 approximately corresponds to the inner diameter of the waveguide 14 . The end 24 of the microwave conductor 16 projects into the interior of the waveguide 14 and is laid there insulated from the walls of the waveguide 14 . For this purpose, for example, gaps may be provided in the walls of the waveguide 14 . According to another example, the microwave conductors 16 are laid within the circuit board substrate 12 so that gaps are no longer required.

A second groove 40 for accommodating a high-frequency chip (not shown) is provided in another area of the front side 18 of the circuit board substrate 12 . In particular, the microwave conductor 16 can advantageously be laid in the connection region 22 or in the inner region of the waveguide 14 by creating a resonator with the groove 30 and the metal coating 32 in reverse or on the rear side. This advantageously enables the adjacent arrangement of high-frequency electronic devices and thereby enables space savings. The second groove 40 can be cast from synthetic resin and thereby improve the mechanical stability and reliability.

Another exemplary modification of a circuit board 10 having a circuit board substrate 12 and a plurality of conductive layers 20 is shown in FIG. 3 . In this example, there are also grooves 30 filled with synthetic resin 36 on the rear side 28 of the circuit board substrate 12 , forming resonators for waveguides (not shown) adjacent to the opposite front side 18 . The microwave conductor 16 extends between the second groove 40 and the connection area 22 . The through-contact 38 is used to form an electrical connection between the metal coating 32 and the connectable waveguide 14 (not shown) in the groove 30, which has a recessed area 34 surrounded by the groove. In one example, two adjacent through contacts 38 are disposed at a distance of less than one quarter of a microwave wavelength. This prevents microwaves from escaping between the through-contacts and causing undesirable losses.

In FIG. 4 , a simplified variant of a circuit board 10 having a circuit board substrate 12 not including a conductive layer 20 is shown. This can allow a simple design and therefore cheap raw materials to be used for the circuit board substrate 12 . For shielding purposes, a metal layer 42 can be coated on the front side 18 of the circuit board substrate 12 . Also visible here are through-contacts 38 for electrically connecting the metal layer 42 to the front side 18 of the circuit board substrate 12 .

Figure 5 illustrates a simplified example of a circuit board 10, here showing a view of the rear side 28 of the circuit board substrate 12. A circularly designed circumferential groove surrounding the recessed area 34 can be clearly seen. Here too, the through-contact 38 is arranged circularly in the recess 30 . In the area where a microwave conductor (not shown) leads on the front side 18 of the circuit board substrate 12 to a connection area (not visible here) on the opposite side of the recessed area 34 , larger through-contacts 38 are arranged. Space 44 to allow microwave conductor 16 to pass through.

An embodiment of a circuit board 10 including a circuit board substrate 12 having a plurality of conductive layers 20 is shown in FIG. 6 . The front side 18 of the circuit board substrate 12 that can be seen here is surrounded by plastic 46, which acts as a housing by its stabilizing effect. Here, the connection area 22 is recessed together with the through-contact 38 and the end 24 of the microwave conductor, so that the tubular waveguide 14 (not shown) can be fixed on the front side 18 of the circuit board substrate with the through-contact 38 . In one example, the circuit board is designed as a planar grid array (LGA). To this end, according to one example, the connection of the high-frequency chip can be routed via wires and through-contacts from the bonding pads to the rear side 28 of the circuit board substrate 12 and connected there, for example, to solder pads (not shown).

A method 100 for manufacturing a resonator for microwaves in a circuit board 10 is shown in FIG. 7 . A non-conductive planar circuit board substrate 12 is first provided (110). In a next step 120 , an annular circumferential groove 30 is produced on the rear side 28 of the circuit board substrate 12 . This can be achieved, for example, by milling or similar methods. In a next step 130 , a microwave reflective coating is applied in such grooves 30 on the rear side 28 of the circuit board substrate 12 and in the areas 34 surrounded by the grooves 30 (recessed areas). In one example, the reflective coating is metallic coating 32 .

According to one example, the reflective coating of groove 30 and the reflective coating of recessed area 34 are electrically connected to each other on backside 28 . Thereafter, in step 140, the through-contact portion 38 is manufactured. These through-contacts extend between the front side 18 of the circuit board substrate 12 and the reflective coating or metal layer 42 in the recess 30 , where the through-contacts 38 are disposed on the front side 18 so that the end face of the waveguide 14 can communicate with the through-contacts 18 . The contact portion 38 is electrically connected. Additionally, optionally, step 150 may be performed in which the circuit board substrate 12 is selectively abraded to recess the area 34 surrounded by the groove 30 in a direction toward the front side 18 . This can be achieved, for example, by milling. In step 160 , the groove 30 and/or the area surrounded by the groove may be coated with a reflective coating and stabilized by filling with synthetic resin. For example, this can be achieved by via-filling-prozess.

Furthermore, it should be noted that "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. In addition, it should be noted that the features or steps described with reference to the above-mentioned embodiments can also be used in combination with other features and steps of other above-mentioned embodiments. Reference signs in the scope of the patent application shall not be construed as limitations.

References to Related Applications This application claims priority from European Patent Application No. 17205156.7, filed on December 4, 2017, the entire content of which is incorporated herein by reference.

10‧‧‧Circuit board 12‧‧‧Circuit board substrate 14‧‧‧Waveguide 16‧‧‧Microwave conductor 18‧‧‧Circuit board substrate front side 20‧‧‧Conductive layer 22‧‧‧Connection area 24‧‧‧End of microwave conductor 26‧‧‧Waveguide front end 28‧‧‧Rear side of circuit board substrate 30‧‧‧Circumferential groove 32‧‧‧Metal coating 34‧‧‧Recessed area 36‧‧‧Synthetic resin 38‧‧‧Through contact part 40‧‧‧Second groove 42‧‧‧Metal layer 44‧‧‧interval 46‧‧‧Plastic 100‧‧‧method 110‧‧‧Steps/Provide 120‧‧‧Steps 130‧‧‧Steps 140‧‧‧Steps 150‧‧‧Steps 160‧‧‧Steps

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Neither the description nor the drawings should be construed as limiting of the present invention. Figure 1 shows a cross-sectional view of a partial area of a circuit board Figure 2 shows a spatial cross-sectional view of a circuit board with waveguides. FIG. 3 shows a circuit board with multiple conductive layers and second grooves. Figure 4 shows a simplified design of a circuit board without a conductive layer. Figure 5 shows the rear side of the circuit board with circular circumferential grooves and through-contacts. Figure 6 shows the front side of a circuit board with a plastic housing and recessed areas for waveguides. Figure 7 illustrates a method for fabricating a resonator for microwaves on a circuit board. Markings are schematic only and not true to scale. In principle, identical or similar components have the same reference numerals.

10‧‧‧Circuit board

12‧‧‧Circuit board substrate

14‧‧‧Waveguide

16‧‧‧Microwave conductor

18‧‧‧Circuit board substrate front side

20‧‧‧Conductive layer

22‧‧‧Connection area

24‧‧‧End of microwave conductor

26‧‧‧Waveguide front end

28‧‧‧Rear side of circuit board substrate

30‧‧‧Circumferential groove

32‧‧‧Metal coating

34‧‧‧Recessed area

36‧‧‧Synthetic resin

38‧‧‧Through contact part

Claims (16)

A circuit board (10) for a radar level measurement device, which includes: a non-conductive planar circuit board substrate (12); a microwave conductor (16) configured on the circuit board substrate (12) for Coupling the microwave signal into the waveguide (14); wherein a circumferential connection area (22) for accommodating the front end (26) of the waveguide (14) is arranged on the front side (18) of the circuit board substrate (12) ; Wherein, the end (24) of the microwave conductor protrudes into the connection area (22), so that the microwave signal can be transmitted from the microwave conductor (16) to the waveguide (14) and can be transmitted from the waveguide to the microwave in the conductor; wherein a circumferential annular groove (30) is disposed on the rear side (28) of the circuit board substrate (12) relative to the connection area (22) in the direction toward the waveguide (14), the The annular groove (30) corresponds to the cross section of the waveguide; wherein, the walls of the annular groove (30) and the rear side (28) of the circuit board substrate (12) are surrounded by the annular groove (30) The area (34) has a microwave reflective coating (32) such that the wall of the annular groove and the area surrounded by the annular groove together form a basin-shaped resonator for coupled microwave signals; the circuit board (10) further comprising through-contacts (38) between the front side (18) of the circuit board substrate (12) and the reflective coating (32) in the annular groove, wherein the through-contacts ( 38) is configured at the front side (18) such that the front end (26) of the waveguide (14) is electrically connected to the through contacts (38). The circuit board (10) of claim 1, wherein the reflective coating (32) is designed as a metal coating. The circuit board (10) of claim 1, wherein the through-contacts (38) are arranged between the front side (18) and the reflective coating (32) in the area of the annular groove, such that The reflective coating (32) can be electrically connected to the waveguide (14). The circuit board (10) of claim 3, wherein the distance between two adjacent through-contact portions (38) is less than a quarter of the wavelength of the microwave. The circuit board (10) of any one of claims 1 to 4, wherein the area of the rear side (28) surrounded by the annular groove (30) is recessed in a direction toward the front side (18). The circuit board (10) of any one of claims 1 to 4, wherein the annular groove (30) and/or the area surrounded by the annular groove (30) is filled with another material. The circuit board (10) of any one of claims 1 to 4, wherein the connection area and the annular groove are designed to be circular. The circuit board (10) of any one of claims 1 to 4, wherein the connection area (22) and the annular groove (30) have a rectangular shape. The circuit board (10) of any one of claims 1 to 4, wherein the circuit board (10) is in the circuit The front side of the board substrate (12) has another groove (40) for accommodating the high-frequency chip, and the microwave conductor (16) extends between the other groove (40) and the connection area (22) . The circuit board (10) of claim 9, wherein the other groove (40) is filled with synthetic resin. A radar level measurement device, which has a circuit board (10) according to any one of claims 1 to 10. A method (100) for manufacturing a resonator for microwaves in a circuit board (10) as claimed in claim 1, comprising the step (110) of providing a non-conductive planar circuit board substrate (12); The step (120) of manufacturing a circumferential annular groove (30) on the rear side (28) of the circuit board substrate (12); on the wall of the annular groove (30) and behind the circuit board substrate (12) The step (130) of coating a microwave reflective coating (32) on the area (34) of the side (28) surrounded by the annular groove (30); between the front side (18) and the annular groove of the circuit board substrate (12) The step (140) of making through contacts (38) between the reflective coatings (32) in the grooves, wherein the through contacts (38) are arranged at the front side (18) such that the front side end of the waveguide The portion (26) can be electrically connected to the through-contact portions (38). The method (100) of claim 12, wherein the step (120) of manufacturing the annular groove (30) further includes abrading the circuit board substrate (12) so that the area surrounded by the annular groove (30) (34) The step (150) of recessing in the direction towards the front side (18). The method (100) of claim 12, wherein the step (120) of producing the annular groove (30) and/or the surrounded area (34) is performed by means of milling or by means of laser. The method (100) of claim 13, wherein the step (120) of producing the annular groove (30) and/or the surrounded area (34) is performed by means of milling or by means of laser. The method (100) of any one of claims 12 to 15, further comprising: filling the annular groove (30) and/or the area (34) surrounded by the annular groove (30) with another material ) step (160).